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工程热力学（英文要点·大三大四）
核心内容
Basic concepts:
In this course, i learned the zero law of thermodynamics, the first law of thermodynamics, the nature of the ideal gas and the thermal process, the second law of thermodynamics, the basic way of heat transfer and so on.
Explanation of concepts:
Basic concepts:
Heat engine: which can transform thermal energy into mechanical energy of the machine, such as steam engine, internal combustion engine and jet engine.
The zero law: if each of the two objects is in thermal balance with the third object, then the two objects must also be in thermal balance.
Thermal balance: when the heat transfer between the two objects, after a time , the two will reach the same temperature, then they are in heat balance.
The first law: when the heat energy and other forms of energy transfer to each other. The total amount of the energy is conservation in this process.
The essence of the first law is the energy conservation law. The expression of the closed system first law of thermodynamics: Q-W=ΔU
It means that the energy enter the system - the energy leave the system = the change of the energy stored in the system
The second law:
Clausius stated(克劳修斯表达): it is impossible to remove heat from low temperature object to high temperature object without causing other change.
Kelvin Planck(开尔文-普朗克表达): it is impossible to take heat from a single heat source and to make it fully converted to work and not to have other effect.
The second law of thermodynamics illustrates the direction, condition and limit of the thermal process in the nature. And it illustrates that the perpetuum mobile of the second kind(第二类永动机can abserb heat energy from single heat source and convert it into mechanical energy 100%) is impossible.
Cannot cycle:
P is the pressure;
V is the volume;
T is the temperature;
S is the entropy(熵) J/K;
Carnot cycle consists of two reversible constant temperature processes（可逆定温过程） and two reversible adiabatic processes(可逆绝热过程):
1-2 constant temperature heat absorption (定温吸热);
2-3 adiabatic expansion (绝热膨胀)3-4 constant temperature heat release (定温放热)
4-1 adiabatic compression (绝热压缩)
The heat efficiency is according to the T1 and T2, and it is none of business of the nature of working medium(工质).
T1: the high temperature heat source.
T2: the low temperature heat source.
T1>T2 the efficiency is always less than 1.
T1=T2 ,ηc=0 so the temperature difference is the requirement when the heat energy transfers to the mechanical energy.
Carnot theorem:
All the heat engines working in the same heat source of high temperature and low temperature heat sources have the same thermal efficiency, it is nothing to do with the work medium;
The thermal efficiency of any irreversible heat engine(不可逆热机) is less than a reversible engine working in the same high temperature and low temperature heat sources.
We know the condition of the heat energy transforming to the mechanical energy and how to improve the heat efficiency.
Basic modes of heat transfer:
Heat conduction(热传导): it is caused by the thermal motion of atoms between objects. It is a heat transfer phenomenon. Such as shaking hands.
Heat convection(热对流): it is caused by the relative displacement of objects. Such as the heat exchange between the indoor and outdoor air.
Heat radiation(热辐射): it is caused by the internal thermal motion of atoms and radiate to the outside. Such as the micro-wave oven. It is use the heat radiation.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：工程热力学
机械设计（英文要点·大三大四）
核心内容
Basic concepts:
In this course, i mainly learned fatigue strength of mechanical parts, mechanical connection, mechanical transmission and bearing.
Explanation of concepts:
Fatigue strength of mechanical parts:
Left is the material fatigue curve.
σmax is the max stress the material holds.
N is stress-number of cycles at the σmax.
People get this curve from lots of experiments. And we can know that we should keep the stress of the material less than the σmax.
For improving the fatigue strength: a、reduce the stress force; b、choose the material with high fatigue strength; c、improve surface quality of parts.
Mechanical connection:
Mechanical connection includes thread connection, key connection.
As for the thread connection, before it works, there should be a pretightening force(预紧力).
Almost all the thread connection should be tightened when we want to use it. So before the thread connection is in the working bearing load, it will be under a force, the force is called pretightening force.
The amount of the pretightening force:
As for the carbon steel(碳钢): F0≤(0.6~0.7)σsA1.(Q235 σs=235MPa)
As for the alloy steel(合金钢): F0≤(0.5~0.6)σsA1.
The σs is the bolt material yield limit(螺栓材料屈服极限).
The A1 is the bolt danger cross-sectional area(螺栓危险截面面积).
The thread includes internal thread and thread connection. And the thread connection includes bolt connection(螺栓连接), double-screw bolt(双头螺柱连接), screw connection(螺钉连接). The thread connection is used for fixing the part which don’t have relative movement.
Tensile strength of bolt danger cross-sectional area(螺栓危险截面抗拉强度):
F0 is the pretightening force.
The d1 is the minor diameter of the bolt.
The [σ] is the Reference tensile strength(参考应力强度).
Key connection(键连接):
There are mainly five kinds of keys: multiple spline(花键), flat key(平键), woodruff key(半圆键), taper key(楔键) and tangent key(切向键).
multiple spline flat key woodruff key
taper key tangent key
Multiple spline: usually used on the interference fit of the gear and the shaft or the coupling and the shaft.
Woodruff key: just like the flat key. But it may make the strength of the shaft low, usually used in some situation transmit small force.
The key connection usually is used to realize the circumferential(周向) fixed between the shaft and the wheel hub to transmit torque(转矩).
Rivet connection(铆接):
Advantage:Process equipment is simple, impact resistance, solid and reliable.
Welding connection(焊接):
Advantage: High strength, simple process.
Cementing connection(胶接):
Advantage:simple process.
Mechanical transmission(机械传动):
Mechanical transmission includes belt transmission, chain transmission, gear transmission and worm transmission(蜗杆传动).
Belt transmission(<7):
Advantage: simple construction, steady transmission, low cost, it has
buffer(减震) which can absorb vibration.
Disadvantage: it has elastic slipping phenomenon(打滑现象) and affect the
transmission efficiency.
Chain transmission(<7):
Advantage: no slipping phenomenon, keep accurate transmission ratio,
compact construction, lower pressure, install easily, can work
in some bad circumstance, such as high temperature or welt.
Disadvantage: the two wheels’ direction must be the same, and the axis of
the two wheels must be parallel, easy to wear and has some
noisy, can’t be used in the wide range ,load change and
high speed transmission.
Gear transmission(single stage<6; double stage=6~30):
Advantage: efficient, compact structure, work reliably, long lifetime, the
transmission ratio is stable.
Disadvantage: high accuracy of manufacture and install, high cost, it is not
suitable for the long transmission distance.
Worm transmission(15~60):
Advantage: it can achieve large transmission ratio, compact structure,
steady transmission fewer noise.
Disadvantage: there is some slipping at the mashing point, easy to wear
lower efficiency.
Bearing(轴承):
It can support mechanical rotary body, reduce the friction, ensure the accuracy of its rotation.
According to the difference nature of friction, the bearing includes sliding friction bearing and rolling friction bearing.
Sliding friction bearing includes radial bearing(向心轴承) and thrust bearing(止推轴承).
The radial bearing is under radial load. Thrust bearing is under axial load.
Application of the sliding friction bearing: high rotate speed, large impact or vibration, in the water or some other circumstances, such as using in the combustion motor aircraft engine, radar.
The structure of the rolling friction bearing includes inner ring, outer ring, rolling body and holder.
The rolling bearing has low friction coefficient, less start resistance. It is standardization.
So the selection, maintain, lubrication are convenient. Is is widely used in common machine.
There are two sealing method: contact sealing(接触式密封), such as sealing ring. Non-contact sealing(非接触式密封), such as gap sealing(间隙密封).
The lifetime calculation formula of rolling bearing:
: the lifetime , the unit is 10^6 round
C: basic rated dynamic load (基本额定动载荷)
P: equivalent dynamic load(当量动载荷)
ε：just a coefficient, as for the ball bearing it is 3, non-ball bearing it is 10/3.
If the we have to consider the temperature, the formula is
The ft is the temperature coefficient, it can be found in the standard table.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：机械设计
单片机原理（英文要点·大三大四）
核心内容
Basic concepts:
In this course, i mainly learned the structure of single chip computer and some basic program of AT89S51.
Explanation of concepts:
Single chip computer is a microcomputer. It has CPS(central processing unit), RAM(random access memory 快取记忆体), ROM(read only memory 只读记忆体), parallel input/output interface(并联I/O接口), serial input/output interface(串联I/O接口), timer(计时器), counter(计数器), interrupt system(打断系统) and system bus(系统总线) on the semiconductor silicon wafer(硅片).
Characteristics of the single chip computer: it is small in size, have lower price, has convenient application and it is stable and reliable.
The single chip computer has wide application. It is used in many electronic products, robots and cars. It has automatic control function by the finished program which is stored in the chip.
Structure of single chip computer:
The Watch dog timer: it is a timer, when the SCM work normally, this timer will be reset after a constant certain time, when the program don’t work normally, it won’t be reset, and it will overflow, and make the program restart. Just like feed a dog.
Timer: to generate precision time pulse to delay or something else to start the period event and count the impulse signal.
In this course, i also learned a little assembly language, but just the very easy part, because we seldom use it.
Here is a simple program in assembly language:
Hexadecimal(16进制) binary system(2进制) decimal (10进制)
START： MOV A,#00H --- #:immediate data H: hexadecimal
MOV R1,#10 ---assign 0 to A and assign 10 to R1
MOV R2,#00000011B ---assign 03H to R2
LOOP： ADD A,R2 ---assign the sum of R2 and A to A
DJNZ R1,loop ---DJNZ: R1 minus 1 and don’t jump if
it is not 0, continue the loop, if
the R1 is 0, next step
NOP ---it means do nothing and go next,
just for holding time, and waiting
for the next order
HERE： SJMP HERE
grade operation code operation date
(标号) (操作码) (运行数据)
Above is a simple circulate program of the single chip computer. It can be used to delay.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：单片机原理
材料成型技术基础（英文要点·大三大四）
核心内容
Basic concepts:
In this course , i mainly learned about the metal structure and metal crystal, casting(铸造) ,metal plasticity(金属塑形成性) and joint forming.
Explanation of concepts:
The metal structure and metal crystal:
This part is introduced in《chemistry of engineering》in detail.
Casting:
Casting is pouring the melt metal into casting mould(铸模) and after cooling we can get the workpiece with certain shape, size and performance. It is a forming method.
Advantage of the casting: low cost, the shape and size of the casting workpiece
is not restricted.
Disadvantage of the casting: misrun(浇铸不满), contraction cavities(缩孔), pore(气孔), flaw of tissue looseness(组织松散), there may be some sinkhole(沉孔), the quality is unstable and the efficiency is low.
The higher the casting temperature is, the better the liquidity(流动性) is. And the liquid metal will fill the mould better.
The pressure is stronger, the liquid will fill the mould better.
Contraction cavity: in casting solidification process(铸造凝固过程), because fo the poor feed, the holes came into being. It often appears in the final solidification parts. When the metal solidification temperature range is wide, it is easy to appear contraction cavity.
The solution of the contraction cavity: we can make the solidification in a certain direction in the mould and add the pressure to feeding to reduce the shrinkage cavity.
Sometimes, there casting stress(铸造应力) in the casting. So we can design the casting structure reasonably or use stress relief annealing.
The air hole is for letting the air in the mould go out.
The pouring gate is the way that the melt metal go into the mould.
We have practiced the casting in the engineering training.
Cast riser(冒口): to prevent misrun and make the contraction cavities into the riser.
Investment moulding(熔模铸造)：using wax make the model like the workpiece, then use mud wrap up the model, then dry it , then the dry mould is baked into a ceramic mould(陶模), after baking, the wax model will disappear, only left the ceramic mould, then casting through the sprue gate we left.
Lost foam casting(消失模铸造):use the wax make the model, brush the fire proof dope on the model, then put it into dry sand, casting under the negative pressure, make the wax model gasify and the melt metal occupy the space of the model, then cool it down.
The metal plasticity:
The metal plasticity include forge(锻造) and stamping(冲压).
The advantage of the plasticity: high material utilization(高材料利用率), high production efficiency(高生产效率).
The principle of plastic forming is the relative sliding in lattice(晶格) between atoms due to the large shear stress.
Free forge: simpleness, be in common use, directly economic, make the billet(坯料) deformation directly. And it is suitable for the single-piece production and small-lot production. The commonly used basic working process of the free forge include:
Die forge: forge which is using the die. It has some advantages , such as high efficiency, high precision(精度). But it is high cost ,too. One of the upper die and the lower die is often fixed, and another one can move.
Stamping: make the sheet metal separation or form. Usually the thickness of the workpiece is less than 4mm.
The advantage of the stamping: easy and simple to handle, high productivity, high material utilization.
The stamping mainly includes three methods: blank(落料), punching(冲孔) and bend(折弯).
The difference between blank and punching: the blank needs the falling part, but the punching needs the remaining part.
Joint forming:
Joint forming is a type of connection of components. Such as welding, glue joint and mechanical connection.
Welding: use the heat energy of the pressure, use or not use the filling material(填充材料) to connect the parts.
Welding mainly includes:
Melt welding(熔焊): melting the metal to connect parts together;
Press welding(压焊): using pressure and temperature to connect the parts;
First using pressure to squeeze the weldments together and close, then the electrode will generate current and the current will go through the weldment, the resistance of the weldment is very big, and it will generate a great amount of heat to melt part of the weldments and joint them together.
Braze welding(钎焊): using the brazing filler metal fill the gaps, the metal has
lower melting point.
Braze welding includes two kinds of welding method, one is the soldering(软钎焊), usually the melting temperature of the alloy is lower than 450℃, the strength of the joint is low. And the other one is brazing(硬钎焊), the melting temperature of the alloy is higher than 450℃, the strength of the joint is high, usually higher than 200MPa. Using to connect the workpieces which bear large force or working in high temperature.
Because of the welding temperature of the brazing welding is not too high, so the joint usually smooth and the tissue and the performance change very little, the deformation of the workpiece is small. Usually used to some place high precision, micro size, complex structure, such as the vacuum vessel and hard allow tool.
Carbon dioxide protection welding: using the carbon dioxide as the protection gas. It is more safe , and can exhaust the air.
Glue joint: use glue to connect the workpieces. It has high production efficiency and low cost.
Mechanical connection: this part is introduced in 《principle of mechanical》
It is easy to repair.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：材料成型技术基础
互换性与技术测量（英文要点·大三大四）
核心内容
Basic concepts:
In this course, i learned about the concept and effect of interchangeability(互换性), shaft-hole fit and choice of fit system(孔轴配合与配合副的选用), geometric tolerance(几何公差) and surface roughness.
Explanation of concepts:
Interchangeability:
The interchangeability is an ability that the size or the function of one product or part can be replaced by another product or part.
Effect of the interchangeability: it is very convenient for the products’ design, manufacture maintain and the production efficiency will be higher and it will reduce the workers’ work, save the cost.
Shaft-hole fit and choice of fit system:
There are three types of fit: clearance fit(间隙配合), transition fit(过渡配合), interference fit(过盈配合).
Dmax and dmax are named upper limit size(上极限尺寸).
Dmin and dmin are named lower limit size(下极限尺寸).
D is the ideal size.
ES=Dmax-D es=dmax-D
EI=Dmin-D ei=dmin-D
ES and es is named upper limit deviation(上极限偏差).
EI and ei is named lower limit deviation(下极限偏差).
If the Dmin≥dmax, EI≥es, then the hole tolerance zone is above the shaft tolerance zone, then this fit is the clearance fit.
Max clearance is Xmax=Dmax-dmin=ES-ei;
min clearance is Xmin=Dmin-dmax=EI-es.
If the Dmax≤dmin, ES≤ei, then the shaft tolerance zone is above the hole tolerance zone, then this fit is the interference fit.
Max interference is Ymax=Dmax-dmin=ES-ei;
Min interference is Ymin=Dmin-dmax=EI-es.
If the Dmax>dmin and Dmin<dmax , ES>ei and EI<es, then this fit is the transition fit.
Hole-basic system(基孔制)
The lower limit deviation of the hole is zero.
Shaft-basic system(基轴制)
The upper limit deviation of the shaft is zero.
Usually we choose the hole-basic system. Because the size of the hole is easy to ensure and to measure. In some special situation, we choose the shaft-basic system, such as in some special structure, we already have a shaft to assemble with several holes. IT is the standard tolerance grades. The alphabet is the basic deviation.
For example,
is the hole-basic system. is the shaft-basic system. H/h is the base.
In the hole-basic system, a~h is the clearance fit, js/j/k/m/n is the transition fit, p~zc is the interference fit.
In the shaft-basic system, A~H is the clearance fit, JS/J/K/M/N is the transition fit, P~ZC is the interference fit.
Geometric tolerance:
After the processed, the actual geometric elements and the ideal geometric elements have some difference in the shape, direction and the position, these difference is the geometric tolerance.
There are four types of geometric tolerance: shape tolerance, direction tolerance, position tolerance and run-out tolerance.
Type of the
tolerance
name
symbol
Shape tolerance
Straightness(直线度)
—
Flatness(平面度)
424815109855
Roundness(圆度)
45085069850
Cylindricity(圆柱度)
Direction tolerance
parallelism（平行度）
Verticality（垂直度）
Slope（倾斜度）
Position tolerance
Position degree（位置度）
Coaxiality（同轴度）
Concentricity（同心度）
degree of symmetry （对称度）
Run-out tolerance
Circular Runout（圆跳动）
Total runout（全跳动）
Closed loop:
09525The dimension chain(尺寸链): when we machine a workpiece, the dimensions of the workpiece will connect as a loop, the finial cimension which is not be labeled is called closed loop.
When the other dimension don’t change, only change one dimension , it its increasing causes the closed loop increasing, it is a increasing link or it is a decreasing link.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：互换性与技术测量
工程材料与热处理（英文要点·大三大四）
核心内容
Basic concepts:
In the course i learned the metal structure and metal crystal, iron-carbon alloy and heat treatment of steel.
Explanation of concepts:
The metal structure and metal crystal:
This part is in the 《engineering chemistry》.
Iron-carbon alloy and iron-carbon phase diagram:
09525In different situations of different carbon contents and different temperature, what is in the iron-carbon alloy is different,too.
Left is a diagram which reflects the material states of the iron-carbon alloy in different situations.
Austenite(奥氏体): face-central cubic structure, usually is the γ-Fe +few C, without magnetism, low hardness have some toughness.
Ferrite(铁素体): a lot C add into α-Fe, body-central cubic structure, can content very little C.
Cementite(渗碳体): high hardness and very brittle.
Pearlite(珠光体):the ferrite and the cementite mixed piece by piece.
Ledeburite(莱氏体): mixture of the austenite and the cementite, hard and brittle.
GS line: when cooling down, the austenite turns into ferrite, when heat up the ferrite turns into austenite.
ES line: the solubility curve of the carbon in austenite, when the temperature is lower than this line, the carbon will separate out as Fe3C from the austenite, and the Fe3C is called secondary cementite. ES line is also called ACm line.
PQ line: it is the solubility curve of carbon in ferrite, when the ferrite cooling down from the 727℃, the solubility of the carbon becomes little. The carbon will separate from the ferrite as Fe3C, which is called tertiary cementite.
The carbon content of the technically pure iron(工业纯铁) is under 0.0218%.
The carbon content of the carbon steel(渗碳钢) is 0.0218%~2.11%.
The carbon content of the white cast iron(白口铸铁) is 2.11%~6.69%.
false
Heat treatment of steel:
Heat treatment of steel is to use hear up, keep warm and cooling to change its internal structure. They can reduce the hardness and reduce or eliminate the internal stress and make the steel have better performance.
There are four basic crafts of heat treatment: annealing(退火), quenching(淬火), normalizing(正火), tempering(回火).
Annealing and normalizing: these two are heating up the workpiece to one temperature, then cool the workpiece to reduce the hardness, eliminate the internal stress. The difference between them is normalizing is to cool the workpiece fast,but the annealing is usually to cool the workpiece slowly the hardness after normalizing is a litter higher than annealing. Normalizing is cooled in the air or blow cold air, is treat the low carbon steel. Annealing is cooled with the furnace. They are all for elimating the internal stress.
Quenching : quenching is to heat up the workpiece higher than AC1(730℃) or AC3(791℃). After the holding temperature, then put the workpiece into the water or the oil to cooling fast. It is often regard as the preparation of the tempering.
Tempering: it is after the quenching, heat up the steel to a temperature under AC1, then cool the steel to the room temperature in a proper velocity to reduce or eliminate the residual stress(残余应力).
Type of the tempering:
1,low temperature tempering: 150~250℃, keep the high hardness, HRC58~64, and high resistance of wearing, mainly for low the quenching stress and brittle. Usually for the high carbon steel workpiece, die the workpiece with high wear resistance.
2,mid temperature tempering: 350~500℃, HRC35~45, high elasticity and yield limit, treat the spring.
3,high temperature tempering:500~650℃, HRC25~35, high strength, good plasticity and toughness, usually called hardening and tempering(调质), using for treating the structure parts, such as the changeable load bars, shafts and bolts.
We once practiced the quenching when we did the engineering training. First , we put the workpiece in the box-type furnace and heat up to 810℃, after two hours of holding temperature, we toot it out and put it into the water to cooling. Then we measured the hardness of the surface of the workpiece.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：工程材料与热处理
金工实习（英文要点·大三大四）
核心内容
Basic concepts:
In this course, we mainly learned how to use several tools which are very popular in factory, such as milling lathe,numerical controlled lathe, numerical controlled milling, drilling, welding, benchwork and non-traditional-machining spark cutting, heat treatment. The numerically controlled lathe programming and numerically controlled milling programming are the key of this course.
We made a frame for candle with other craftwork. The lampstand of the frame is using the milling, drilling and benchwork. As for the body of the frame, we used the lathe.
We finished out work all in the engineering training center of our school. And teacher ave us grade based on our theoretical exam and our production.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：金工实习
MATLAB 基础及应用（英文要点·大三大四）
核心内容
Basic concepts:
Matlab is a software, we can use it to program and draw the diagrams. It is similar to the C language. In this course, we learned some simple programs of the Matlab.
Explanation of concepts:
We can write the program in some files and then save the files, and when we want to use it. We can use it directly in Matlab. For example, we can write a program in a file,
And we open the Matlab and type in
-6096049530>>program1 → we only need to type
radius= in the file name.
1
area=3.1416 → it can figure out the
result.
Also, it can draw some diagrams. The order bar can dram the bar chart. The order pie can draw the pie chart. The order area can draw the line chart. The order stem can draw the stem chart. For example,
Application: we can use the tool box of Matlab to solve mechanical optimization design, linear programming problems and nonlinear programming problems.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：MATLAB 基础及应用
数控技术（英文要点·大三大四）
核心内容
Basic concepts:
In this course, I mainly learned the classification of digit control system, digital controlled lathe programming, digital controlled milling machine programming and the interpolation calculation principle(插补原理).
Explanation of concepts:
Digit control technology is a kind of method using of digital information to control the machine movement and machining process. It has high accuracy and high efficiency. And it is very suitable for the mass production(大量生产).
Classification of digit control system:
The digit control system mainly can be divided into three kinds:
1, open loop serve system(开环);
2, closed loop serve system(闭环);
3, semi-closed loop serve system(半闭环/半开环).
There is no feedback and no position measuring element in the open loop serve system. The system has the one-way instruction flow(单向指令流), it is cheep, convenient and the structure of it is simple.The simplified structure is following:
As for the closed loop serves system, it has feedback and position measuring element.the position measuring device is installed on the operating platform. When it measures the actual displacement of the operating platform, it will feedback the signal to the comparator to compare with the command signal, then control the serve drive motor with the difference valve until the difference value turn into zero. This kind serves system has very high accuracy,but expensive of course.
As for the semi-closed loop serve system, the measuring device is not to measure the displacement of the operating platform directly, but by measuring the angular displacement of the motor or the screw to measure the displacement of the operating platform indirectly. And the operating platform is out of the feedback loop. Lower accuracy than the closed loop serve system,but easy to equipment install and trial run, and the cost is lower,too.
Digital controlled lathe programming:
We use FANUC programming language, which is widely used in china.
For example,
In FANUC, we use the G code to write the program.
First, we need to know that in G code, the code start with G is the preparatory function(准备功能), F is the feed function(进给功能), S is the speed function(速度功能), T is the tool function(刀具功能), M is the auxiliary function(辅助功能).
We process the workpiece from right to left, and we use the external turning
Tool. We choose the workpiece coordinate system origin at the centre of the left end surface of the workpiece. The cutting starting at the point (200,350), the speed of main shaft is 630r/min, and the feed velocity is 0.15 mm/r.
Following is the program:
O0020 --- program name
N01 F50 X200 Z350 --- G50 tool offset(刀具偏置)
N02 S630 T0101 M03 --- M03 main shaft start to rotate
clockwise; S630 the speed of main
shaft is 630 r/min
N03 G00 X50 Z76 --- move near to the workpiece
N04 G00 X50 Z75 --- G00 point location fast moving
N05 G01 X80 Z60 --- G01 linear interpolation
N06 Z50
N07 G02 X80 Z40 R70 --- G02 clockwise circular interpolation
the X and Z is the end point coordinate
N08 G01 X80 Z30 linear interpolation
N09 X85 --- the diameter of workpiece is Ф85
N10 G00 X200 Z350 M05 T0100 --- make the tool goes back to the start
To the start and stop the main shaft
Tool retract
Digital controlled milling machine programming:
The workpiece is 180*90*120mm
A(0,0) B(0,40)
C(15,70)D(45,70)
E(100,60) F(150,40)
G(170,40) H(170,0)
We choose point A as the workpiece coordinate system origin. The three holes are already finished and we can use the two small ones to locate the workpiece, and compress the workpiece with the big hole. We choose the milling cutter with diameter is 10mm. The adjusted cutter point is (-25,10,40). The move path:
adjusted cutter point---B---C---D---E---F---G---H---A---adjust cutter point
Following is the program:
O0020 program name
N01 G92 X-250 Y10 Z40 ---G92 present register
N02 G90 G00 Z-16 S300 M03 ---G90 absolute coordinate
G00 point location
M03 main shaft start to rotate clockwise
N03 G41 G01 X0 Y40 F100 D01 ---G41 cutter radius left compensation
Loot at the direction of the tool moving,
the tool is on the left of the workpiece
D01 all the diameter of the cutter from the
system data which we saved before start
N04 X15 Y70
N05 X45
N06 G02 X100 Y60 R40 ---G02 clockwise circular interpolation
The number follow the R is the radius
N07 G03 X150 Y40 R60 ---G03 anti-clockwise circular interpolation
The X and Y is the end point coordinate
N08 G01 X170
N09 Y0
N10 X0
N11 G00 G40 X-25 Y10 Z40 ---G40 cancel the cutter compensation
The cutter back to the origin point
N12 M30 ---M30 stop the program and return
the cutter compensation(刀补):
The system can calculate the path of the cutter center as the cutter has radius. So we can program directly without considering the radius of the cutter if we use the cutter compensation.
G41 is the left cutter compensation.
G42 is the right cutter compensation.
Interpolation calculation principle(插补计算原理):
When the machine process the workpiece, the oblique line and the circle which the tool move is not smooth, it is fold line(折线), the interpolation calculation principle is help us know how can we get the fold line.
Point-by-point compare method(逐点比较法):
the Xe and Ye is the point we want to get.
We can bring the x and y into the formula and get the F.
If F≥0, then the x=△x+1, y=y;
If F≤0, then the x=x, y=△y+1.
Digital differential analyzer(DDA数字积分法):
First, we should define the register digit, then we define the change value of the x and y. The principle of DDA is when the valve in the register is larger than the register digit, it will overflow(溢出), and the accumulator(累加器) will add a change value of the x or y. For example,
The register digit is 8 , the start point is (0,0), end point is (4,6), and the change value is 2.
time
x
△x
y
△y
point
1
0+4=4<8
0+6=6<8
(0,0)
2
4+4=8+0
+2
6+6=8+4
+2
(2,2)
3
0+4=4<8
4+6=8+2
+2
(2,4)
4
4+4=8+0
+2
2+6=8+0
+2
(4,6)
The DDA is easy to realize multicoordinate(多座标) linkage, easy to realize the interpolation of high order curve, and speed of operation is high.
Circular interpolation principle(圆弧插补原理):
Start point A(x0,y0), end point(xe,ye), radius R, present point(xm,ym).
We can calculate the curve according to the above pictures.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：数控技术
机电传动控制与 PLC（英文要点·大三大四）
核心内容
Basic concepts:
In this course, i mainly learned the load characteristic of the electric mechanical drive system, the conditions of electric mechanical system stable operation, mechanical characteristic of mechanical machinery, mechanical characteristic of separately excited DC electric motor(他励直流电机including starting characteristic, speed control characteristic,braking characteristic),mechanical characteristic of three-phase asynchronous electric motor,basic structure of the PLC, ladder diagram and some basic instruction list programming language.
Explanation of concepts:
The load characteristic of the electric mechanical drive system is the function relationship between the load torque and rotational speed on the motor shaft.
There are mainly four types load characteristics,constant torque type,constant power type, out-central type(离心型),linear type.
The conditions of electric mechanical system stable operation:
, the mechanical character curve of motor n=f(TM) and the load character curve n=f(TL) have intersection point.
2,when the rotate speed is larger than the speed at the balance point, if there is a disturb which makes the rotate speed n larger,when the disturb disappears, the TM<TL;if it make n smaller, when the disturb disappears ,the TM>TL.
The DC motor:
The structure of the DC electric machinery:
The working principle of the DC electric machinery:
The electric motor have two pole. The armature winding is a winding, and the two ending of the winding is connected on the two commutator bars, and the commutator bars connect with the electric brush. When the electric machinery work as the electric motor, the power source give the winding a current, and the winding is between two poles. When there is a current in the wire, and the wire is in a magnetic field, there will be a force acting on the wire, the force is called Ampere force .In the left picture, we can see the Ampere force is toward left, so the winding will rotate anticlockwise. When the winding rotates 180°, the commutator bars will change the electric brushes which they are connected with. So the current in the winding will change its direction, and make sure the Ampere force keep the winding rotating anticlockwise.
When the electric machinery works as a generator, there will be a external force making the winding rotating in a direction, and makes it cut the magnetic line of the magnetic field. So there will be a current in the winding, the electricity is generated.
Left-hand law: using the left hand, the finger towards to the direction of the current, then let the magnetic line through the palm, then the direction of the thumb is the direction of the force.
The right-hand law is about the direction of the current.
The electromotive force between the two electric brushes is always expressed as:
E--electromotive force;
Ф-- the magnetic flux(磁通量) of a couple of poles;
n--the rotating speed of the armature(电枢);
Ke-- a constant relating to the structure of the electric machinery.
The electromagnetic torque of the electric machinery:
T--electromagnetic torque(电磁转矩);
Ф--the magnetic flux of a couple of poles;
Ia--the current of the armature;
Kt--a constant relating to the structure of the electric machinery, Kt=9.55Ke.
The mechanical characteristic hardness:
The larger is β, the softer the mechanical system is .
Mechanical characteristic of DC electric machinery:
Mechanical characteristic includes intrinsic mechanical characteristic and artificial mechanical characteristic.
The intrinsic mechanical characteristic is the characteristic when the electric machinery is working under the rated voltage(额定电压) and rated magnetic flux(额定磁通量). We can get it from the parameters wrote on data plate.
The artificial mechanical characteristic means that the mechanical characteristic when the voltage and the magnetic flux are not the rated value, and there is a resistance in series with the armature circuit.
1,when there is a resistance in series with the armature circuit:
The function of the artificial mechanical characteristic is :
With the increasing of the Rad, the system is more and more soft.
2,when change the voltage of the armature:
081915
When , and change the voltage of the armature:.
3,when change the magnetic flux:
When and change the magnetic flux Ф:.
The electric motor can be divided into four kinds by the excitation method(励磁方法):the separately excited motor(他励电动机),shunt motor(并励电动机), series motor(串励电动机) and compound motor(复励电动机). We mainly learned the separately excited motor. The other three kinds are not involved.
The starting characteristic of the separately excited motor:
The starting of the separately excited motor means connect the motor into the electric circuit, make the rotator(转子) rotate and get the rated speed. The starting current is . Before the rotator rotate, there is no inductive reactance in the armature, so the current is very large, can be 10~20 times of the rated current, which may burn out the circuit. And the starting torque will be very large, which may hurt the transmission element. So the separately excited motor can not be started directly. There are mainly two starting methods, one is buck starting(降压启动) and another is external resistance starting.
The inductive reactance(感抗): when there is current through a winding, there will be a magnetic field, and the field will generate a current in the winding too, and the current generated is opposite to the original one.
1,The buck starting:
The buck starting means when we want to start the motor, we can make the voltage lower than the rated voltage, and add the voltage with the increasing of the rotating speed of the motor until the voltage meet the rated voltage.
2, The external resistance starting:
The external resistance starting means we can connect external resistance into the starting circuit, and when we want to start the motor, we make the current through the resistance, and when the rotating speed is high enough, we make the resistance cutting-out(短路), and then the rotating speed will meet the rated speed.
and we can make more resistances in series in the circuit, and make them cutting-out one by one, which will make the starting better. The normal starting have three or four step.
Such as the motor in the factories need to be started quickly, so there will be only one external resistance. But the elevator need to move smoothly, so there will be many external resistances.
Speed control characteristic:
Speed regulation of the motor is to change the stable speed of the motor under some load.
The speed regulation and the speed changing is two different concepts. The speed changing is because the change of the load. And the speed regulation is because the artificial adjusting, such as adjust the resistance in series with the armature.
A, change the resistance which is in series with the armature:
We can change the resistance in series with the armature to change the stable speed of the motor, just like the left picture. The A-B-C is the changing step.
But this way has many disadvantage:
1, when the resistance is larger , the hardness of the system is softer, and the stability of the system is lower;2, when there is no load or there is small load, the range of the changing of the speed is small;3, it is hard to realize the stepless speed regulating（无级调速）. And the starting resistance can not be the regulating resistance, or it will be burned out.
B,change the voltage of the armature:
Under the load torque TL, when we add different voltage UN, U1,U2,U3, we can get different rotating speed na,nb,nc,nd, and realize the regulation of the speed.
When the first voltage is U1, and the rotating speed is nb, the torque is TL, we add the voltage to UN, then the T will suddenly add to Lg=(UN-Eb)/Ra. Then the characteristic curve will change along the curve of UN and the rotating speed will add to na.
The characteristic of this way:
1,when the voltage change continue, can realize the stepless speed regulating, but usually the speed must lower than the rated speed.
2,the regulation characteristic of the speed is parallel with the original characteristic, so the hardness of the mechanical characteristic is not changed, the stability is high , and the speed regulation range is large.
3,when we regulate the speed, the current of the armature is not concerned with the voltage U, and the Ф=ФN, so the torque of the motor is not changed, the regulation is constant-torque regulation of speed.
4,we can start the motor by regulating the voltage of the armature.
C,change the main magnetic flux of the motor:
We know that under a load power PL, change the main magnetic flux can change the rotating speed, and realize the regulation of the speed.
The regulation step is like the left picture.
When we want the speed down, it will change along c-d-b. When we want the speed up, it will change along b-e-c.
The characteristic of this way:
1,can realize smooth stepless regulating speed, but can only adjust the speed higher than the rated speed.
2, the regulation characteristic of the speed is a little softer, and limited by the direction-change condition of the motor, the speed of simple separately excited motor can not higher than the 1.2 times of the rated speed, so the regulating range is not big. If we use special material to product regulation motor, the range can be larger, but this kind of motor is big and expensive.
3, this kind regulation method does change the power, so this is constant-power regulation of speed.
Braking characteristic(制动特性):
This part is not important, and we only learned some concepts of it.097155
There are mainly three kinds of braking method:
1,feedback braking(反馈制动): feedback the mechanical energy of the motor absorbing to the power grid(电网) or resistors. Save energy, but not safe.
2,reverse connection braking(反接制动): change the direction of the supply voltage, can make it stop quickly.
3,dynamic braking(耗能制动): change the supply voltage to 0, then in series a resistor to consume the energy. Safe and high accuracy.
Mechanical characteristic of three-phase asynchronous motor(三相异步电动机):
The structure of the three-phase asynchronous motor:
The work principle of the three-phase asynchronous motor:
The working principle of the treephase asynchronous motor is similar to the DC electric machinery, but the what the three-phase asynchronous motor using is the three-phase alternating current(三相交变电流). There are 120-degree phase difference between each of the current of the phase:
It is also the Ampere force makes the rotor rotate.
The direction of the rotating of the rotor and the magnetic field is the same, but the speed of the rotor n can’t be the same as the magnetic field n0, n<n0. So the slip ratio is showing the difference degree of the n and n0: .
Electromagnetic torque and mechanical characteristic of the three-phase asynchronous motor:
The electromagnetic torque:
It is one of the most important parameter of the three-phase asynchronous motor, it is generated by the effect of magnetic flux of each pole and the current of rotor I2. The phase of the current of the rotor I2 is behind the electromotive force E2 at φ2, so the electromagnetic torque is:
KT is a coefficient which is relative with the structure of the motor.
Mechanical characteristic:
Under a certain power source voltage U1 and the resistor R2, the curve of relationship between the electromagnetic torque and the slip ratio(转差率) T=f(s) or the curve of the relationship between the rotating speed and the electromagnetic torque n=f(T) is called the mechanical characteristic curve.
The function of the torque T:
P2 is the mechanical power of the main shaft of the motor;
N is the rotating speed of the main shaft of the motor.
The rated torque is .
The max torque is .
X20 is the inductive reactance(感抗).
The starting torque is .
The starting of the the three-phase asynchronous motor:
There are two methods of the starting of the the three-phase asynchronous motor: direct starting and the buck starting.
Direct starting:
If we start the motor directly, the method is easy, but the starting current is very large and it make the voltage of the starting is very small, which may affect the work of the motor.
Buck starting:
The direct starting make the voltage of the circuit go down a lot, so we can choose the buck starting, to reduce the starting current. There is a very useful starting method of buck starting: star-delta starting.
If the motor is working under the delta winding(三角形绕组), then when we start the motor we can change the winding into the star winding(星形绕组), which can make the voltage of each phase is the square root of 1/3 times of the normal voltage, and the current is 1/3 of the normal current. But this way only fit the non-load starting or the light-load starting. When we start the motor, we connect the Q3 and Q1, when the speed is near the rated speed, we cut off the Q3 and connect the Q2.
The speed control of the three-phase asynchronous motor:
There are mainly three speed control method of the the three-phase asynchronous motor, frequency control speed regulation,pole-changing speed regulation and variable slip ratio speed regulation.
The frequency control speed regulation is usually used in air conditioner, fridge and the washing machine.
The pole-changing speed regulation is usually used in milling machine and some other manufacturing machine.
The variable slip ration speed regulation is usually used in erecting equipment (起重设备).
The braking of the three-phase asynchronous motor:
There are mainly three method of the braking of the three-phase asynchronous motor, feedback braking(反馈制动), the reverse connection braking(反接制动) and the dynamic braking(耗能制动). They are similar to the braking of the DC electric machine.
PLC:
Basic structure of PLC:
We mainly used the S7-1200 type PLC, so this part are all based on this type PLC.
,CPU: central processing unit, including microprocessor (chip) and memorizer.
CUP constantly gathers the input signal, execute the user programs,refresh the output of the system. The memorizer is used to store the programs and data.
2,the input module and the output module:
The input module is used to receive and gather the input signal, such as the signal of switch, current and voltage signal.
The output module is used to control the electromagnet(电磁铁), electromagnetic valve(电磁阀), indicator light(指示灯) or numerical display device.
The input and the output module together are called I/O module. The digital input and digital output module are called DI and DO module. The analog input and analog(模拟输入和模拟输出) are called AI and AO module. They are all called signal module, and SM for short.
3,communication module:
The PLC can add three communication module at most, can use ASCII communication protocol, USS drive protocol,Modbus RTU master protocol and Modbus RTU slave station protocol.
4,programming software, used to writing the program of the PLC.
The characteristics of PLC:
1, the method of programming is easy to learn.
2, have many function, and the ratio of the performance and the cost is high.
3, hardware is complete, easy to use, and can fit different situation.
4, high reliability, good capacity of resisting disturbance(抗干扰能力).
5, need less work to operate it.
6, less work to fix it, easy to fix.
7, small volume, small energy consumption.
Application of the PLC:
Logical control, motion control, communication and networking.
Ladder diagram:
Ladder diagram is a widely used PLC programming language. It is audio-visual and easy to understand. It consists of contact(触点),coil(线圈) and order, expressed by the box square frame.
The contact represents the input signal, such as the switching signal.
The coil represents the output result, such as the indicator light.
The square frame represents the command, such as the timer and counter.
The analysis order is pom up to down, from left to right.
For example,
This is a typical circuit, the start-retention-stop electric circuit(起保停电路).
The | | is normally open contact(常开触点).
The |/| is normally closed contact(常闭出点 if we touch it , the circuit will cut off).
And the ( ) is the coil.
And we can rewrite it into instruction list programming language.
LD I0.0 LD -- load, is equal to the “| |”;
O Q0.2 O -- or;
AN I0.1 AN -- and not;
= Q0.2 = -- output;
And there are some other signals, such as,
A -- and; ON -- or not; LDN -- negation then load, is equal to the”|/|”.
So the function of this circuit is to start the motor when we push the start button and keep it run until we push the stop button.
When we push the start button, the I0.0 closed, and I0.1 is already closed, then the line is conducting, and the coil Q0.2 is electrify. This is the start function. Meanwhile , it is normally open contact Q0.2 is connect and when we relives the start button, the I0.0 is cut off, but the Q0.2 is still connecting, so through the OR gate, the circuit is also running. This is the retention function.
Until we push the stop button, the I0.1 cut off, then the coil Q0.2 and Q0.2 are both cut off, when we relives the stop button, they will still keep cutting off situation, so it will not connected, this is the stop function.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：机电传动控制与 PLC
生产实习（英文要点·大三大四）
核心内容
Basic concepts:
In this course, we mainly visit some factories and companies to know more about the production in factory and how to design the products.
Explanation of concepts:
We mainly visited the Chery automobile company .The Chery automobile company is located in Wuhu, Anhui province.
We mainly visited the engine production workshop and the assembly workshop. In the engine production workshop , there are mainly five production lines, the cylinder production production line(引擎缸体线), the cylinder head production line(缸盖生产线), the cam rough machining production line(凸轮粗加工生产线), the cam finishing machining production line(凸轮精加工生产线) and the assembly production line(组装线). First two production lines are all form a German company named Cross Huller. The cylinder production line is a flexible production line(柔性生产线) which consists of high speed machining center(高速加工中心), cleaning machine(清洗机), assembly machine(装配机) and some other devices. It can product many kinds of cylinder which belongs to many kinds of gasoline engines(汽油机引擎) and diesel engines(柴油机引擎). As for the cylinder head production line, it can product self-contained complete cylinder heads of the cylinders. The rough machining production line consists of some Chinese product machine. The finishing machining production line is buying from a German company named Junker. And the assembly production line is buying from a Italian company named COMAU.
In the assembly workshop, the assembly production line is almost full automatic, it consists of many mechanical arms and conveyer belts. The efficiency of the assembly production line is very high.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：生产实习
液压与气压传动课程设计（英文要点·大三大四）
核心内容
Basic concepts:
In this course, i mainly made a course exercise of hydraulic transmission. The topic of my course exercise is design a hydraulic system of a water gate.
Explanation of concepts:
In this course , we work by group, each group has about 7 student. And we have our own work to do. For me, my work is to model the 3D workpiece. I also know the step of the whole work, but i don’t know the detail of many parameters, it is a long time ,you know, and the design has been given to my teacher after the class, and my work need not to know too know every parameter. So lets talk about the step of the design.
First , we should know the data of the requirement, then choose the hydraulic pump;
Second, we have choose the hydraulic, then we should design the hydraulic circuit and draw the hydraulic principle diagram;
Third, we should choose other hydraulic elements according to the requirement and the data of the hydraulic pump;
Forth, we have know all the hydraulic elements, then we should design the hydraulic manifold block(液压集成块), this is my task.
These four steps are the whole work of this course.
As for my task, we should to know what is the hydraulic manifold block. If we use the classical way to design the hydraulic system, we should use tube, and if a system is very complicated, there will be so many kinds and amount of tubes, and arranging the tube and the hydraulic elements in the space will be a very big problem. So we can drill holes on a cubic steel block as the tubes and fix all the hydraulic elements on the surface of it. So the cubic steel block is the hydraulic manifold block. Using it can avoid the complicated tube arrangement, but we should arrange the holes on it ,too.
First, we may use more than one block, in this course, we use four block.
Second, we should redraw the hydraulic principle diagram, to rearrange the elements more suitable for the block.
Third, every block has three main holes, common pressure oil port(公用压力油口), common oil return port(公用回油口) and common leakage oil port(公用泄漏油口). We should arrange the elements on the front, back and the right side. On the right side, we always arrange the pressure control valve and the flow control valve. On the front, we always arrange the direction control valve, of course if there are too many valves on the right side, we can adjust some of them to the front. As for the back, we always arrange some direction valve which don’t need to be controlled. On the left side, we always don’t arrange valves, but some measuring devices and auxiliary oil ports.
Forth, we should arrange the other holes as the tubes connects the hydraulic elements. They should be straight as far as possible. And the position of the holes are decided by the position of them on the hydraulic elements. All the elements are standard parts , the position of the ports on them can be found on the book, we just need to look at the books and find them.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：液压与气压传动课程设计
机械制造技术基础课程设计（英文要点·大三大四）
核心内容
Basic concepts:
This course is for designing a milling jig for a workpiece.
Explanation of concepts:
Above picture is the milling jig , and the red part is the workpiece, the black part is the feeler block(对刀块).What we have to do is to design the jig to fix the workpiece.
Fist, we have to know that the jig need to limit the degree of freedom of the workpiece, and all the six degree of freedom need to be limited. So at the left of the jig, i choose a long V-type block . And on the right, is a movable V-type block, which have thread on it and can clamp the workpiece by turn the hand bar. These two parts limit five degree of freedom, as for the left one, i choose to use the self-support ball(自支撑球体). The self-support ball can’t and only can’t move up and down, and it can make any movement on the other direction, so it can only limits one degree of freedom. Then the six degree of freedom are all limited. The two U-type grooves on the blue part is for fixing the jig on the milling machine. All the parts are the standard parts, the parameter of them can be found on the book.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：机械制造技术基础课程设计
机械制造技术基础综合实验（英文要点·大三大四）
核心内容
Basic concepts:
This experiment is a casting experiment, we build casting moulds, and cast simple parts. All these work are making in our engineering training center.
Explanation of concepts:
The mould part are made by us, the casting part is made by our teacher for our safety.
First we should make a mould. We should put the drag box on the operating platform first, then put some wet sand in it, then compact it. Then we put the model of the workpiece in the drag box on the compacted sand, and the small part of the model should toward down. Then we fill the drag box to full with wet sand, and compact it. After that, we clean the sand over the top plane of the drag box and make the top plane of the sand smooth. Then we put some tap sand(分型砂) on it . And stand a tube beside the model. Then we put the cope box on the drag box, and fill it with wet sand and compact it, too. Then clean the top plane of the cope box and make some air hole on it. Then take out the tube in it , the pour gate is formed. Then we make a sign on the cope box and the drag box , for assembling them again. Then we put the cope box away from the drag box, finish the pouring gate in the drag box, and take the model out . Then we can assemble the two box again. Last, our teacher pours melted metal in to the mould through the pouring gate.
Measuring the hardness of the workpiece:
Rockwell hardness(洛氏硬度)：when the HB is larger than 450, we use HR, usually is using a diamond cone with 120°apex angle, press it into the surface of the measured workpiece under a certain load and keep it a certain time, and then get the hardness through measuring the depth of the indentation.
HRA D+588.4N for hard alloy, steel sheet.
HRB 1.5875mm steel ball+980.6N for some soft material, mild steel.
HRC D+1471N for casting iron, quenching steel.
Brinell hardness(布氏硬度): press a material ball into the surface of the measured material.
HBS quenching ball for the material whose hardness is lower than 450, such as mild steel.
HBW hard alloy ball for the material whose hardness is lower than 650.
170 HBS 10/1000/30 10mm d quenching ball, 1000Kg pressure force, metain 30min the HB is 170.
Vickers hardness(维氏硬度): with a pyramis diamond, with 136° angle between face and face, press into the surface.
185 HV5 185 is hardness. 5 is the load, 5Kg.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：机械制造技术基础综合实验
机械制造技术基础（英文要点·大三大四）
核心内容
Basic concepts:
In this course, i mainly learned what is productive process, what is engineering progress, the types of manufacturing and the datum which are used in engineering progress. Then i learned the process of metal cutting, the methods and devices used in machine manufacturing and fixture.
Explanation of concepts:
Production process(生产过程): all the processes from the raw material into the factory to the end product comes out.
Engineering process(工艺过程): in the production process, all the change of the workpiece.
Types of manufacturing: single-production production, volume production, mass production.
Datum:
The datum(基准) ,which is used in engineering process, is called engineer datum(工艺基准). Include process datum, location datum, measuring datum and assembly datum.
Process datum(工序基准): used to determine the basis of the surface dimensions(加工表面尺寸), shape and position of the process.
Location datum(定位基准): used as a reference for locating.(may not exist)
Measuring datum(测量基准): during or after the manufacturing of the workpiece , the datum used for measuring the size and shape.
Assembly datum(装配基准): a datum used to determine the relative of the part of component in the product when assembly.
Metal cutting process:
The basis of cutting:
Vc : cutting velocity, the velocity of the main cutting edge relative to the workpiece.
Vf : feed velocity, feed is the motion making the machined surface complete. The velocity of feed called feed velocity (mm/r).
There is a formula for the Vc:
n: rotate speed of the workpiece
d: max of the diameter of the workpiece
Three keys of cutting: cutting velocity Vc, feed quantity, back engagement of the cutting edge(背吃刀量).
Feed quantity: the relative displacement between the tool and workpiece on the feed movement direction.
Back engagement of the cutting edge: it is the vertical distance between the machined surface and waiting machining surface.
dw is the diameter of the waiting machining surface.
dm is the diameter of the machined surface.
The structure of the cutting tool:
Rake face(前刀面):the cutting chips flow along this surface;
Major flank(主后刀面): the opposite surface of the transitional surface of the workpiece;
Minor flank(副后刀面): the surface which is opposite to the machined surface of the workpiece;
Major cutting edge(主切削刃): the intersecting edge of rake face and major flank, used to finish the cutting work;
Minor cutting edge(副切削刃): the intersecting edge of rake face and minor flank, working with the major cutting edge to finish the cutting work , then the machined surface is finished;
Tool nose(刀尖): a cutting edge connecting the major cutting edge and the minor cutting edge.
When only the major cutting edge involves into the cutting work, it is called free cutting, or it is called non-free cutting.
Annotation angle of cutting tool(刀具角度标注):
1, base plane(Pr 基面): the plane through a specified point on the major cutting lip and is vertical to the direction of the cutting velocity.
2, cutting plane(Ps 切削平面): the plane is through a specified point on the major cutting edge and is tangent to the major cutting edge, meanwhile the plane is vertical to the base plane of that point.
3, tool orthogonal plan(Po正交平面): the plane is through a specified point on the major cutting edge and it is vertical to the base plane and cutting plane of that point.
There are five annotation angles.
1, rake angle(γ0前角): the angle between the rake face and base plane, which is measured in the orthogonal plane. When the rake face is downside, it is positive, or it is negative.
2,clearance angle(α0后角): the angle between the major flank and cutting plane which is measured in the orthogonal plane usually it is positive.
3, major cutting edge angle(Kr主偏角): the angle between the projection of the main cutting edge on the base plane and the direction of the feed motion, which is measured in the base plane.
4,minor cutting edge angle(K’r副偏角): the angle between the projection of the minor cutting edge on the base plane and the negative direction of the feed motion, which is measured in the base plane.
5, tool cutting edge inclination(λs刃倾角): the angle between the main cutting edge and base plane, which is measured in the cutting plane, when the tool nose is the highest point, it is positive.
Tool material:
We need high hardness and wear resistance , enough strength and toughness, and high heat resistance material. Such as high-speed steel(W18Cr4V), hard alloy ,cubic boron nitride(CBN立方氮化硼) and diamond.
The deformation of metal in cutting process:
068580Ι, first deformation area: the metal moves toward right and into AO, start to deform. When it get MO, the shear slip is completed. The area between AO and MO is the first deformation area. The main character is shearing deformation along the slip line and the work hardening(加工硬化).
ΙΙ, the second deformation area: the chip go out along the rake face , the rake face squeeze and rub the chip, make the area of the chip next to the rake face become metal fibrosis(金属纤维化).
ΙΙΙ, the third deformation area: the machined surface is squeezed and rubbed by the flank, and become metal fibrosis and work hardening.
The built-up edge(BUE积屑瘤)：
In the cutting process, there is a strong friction between the cutting chip and the rake face, when the temperature and the pressure is high, the cut material will weld on the rake face, and it will make the temperature and the pressure higher, there will be more and more material weld on it, then the major cutting edge will be thicker, it will become the built-up edge.
The built-up edge will make the rake angle larger, lower the cutting force, make the cutting thickness larger , make the surface quality lower, make the life of the cutting tool shorter.
If we want to avoid the built-up edge, we should choose the right cutting speed, avoid the speed that may cause the built-up edge, choose good-quality cutting fluid(切削液), choose larger rake angle, make the pressure between the chip and the rake face lower, and choose the high-hardness material,which may cause less work hardening.
We use the medium carbon steel as an example, when the cutting speed is lower than 2m/min, there will be no BUE; when the speed is 2~30m/min, the temperature of cutting is 300℃, the BUE is largest; when the speed is 120m/min, the temperature is higher than 800℃, the BUE will disappear.
So usually , under the maximum temperature the tool can hold, improve the velocity of cutting as fast as possible, or using the very low speed.
Types of cutting chip(切屑类型):
1,continuous chip(带状切屑): the inside of the chip is smooth and the outside is lanose(毛绒状). Plastic metal, the cutting thickness is small, high speed and the rake angle is large.
2,segmental chip(节状切屑): the outside is like serration(锯齿) and inside have crack(裂纹).Cutting speed is low, cutting thickness is large, rake angle is small.
3, granular chip(粒状切屑): the cutting force on the shearing plane is larger than the breaking strength of the material, the element of the chip fall from the workpiece.
4,breaking chip(崩碎切屑): when cutting brittle metal(脆性金属), the chip will fly away from the workpiece.
Controlling the type of the chip:
1,use chip breaker(断屑槽);
2,change the angle of the cutter, make the major cutting edge angle larger, make the rake angle smaller;
3,change the cutting quantity, make it small.
Cutting force(切削力):
F(resultant force合力): the vector sum of the Fp , Fc and Ff.
Fp(back force背向力): parallel to the base plane, vertical to the feed direction.
Fc(major cutting force主切削力): vertical to the base plane.
Ff(feed force进给力): parallel to the base plane, parallel to the feed direction.
Fc>Ff>Fp Fp=(0.15~0.7)Fc Ff=(0.1~0.6)Fc
The cutting force is relative to the material of the workpiece, cutting quantity, the geometric parameter of cutting tool, cutting-tool wear, cutting fluid(切削液) and the material of the cutting tool.
Cutting heat(切削热):
In the cutting process, 98%~99% of the energy change into cutting heat.
The elements affect the abstract heat:
1, thermal conductivity(传热系数) of the workpiece;
2, thermal conductivity of the cutting tool;
3,medium around it.
Life of cutting tool:
The time from the tool begin to work until it get the wear stander.
,,, are the coefficient, can be found in tables in the books.
Choice of the geometric parameters of cutting tool:
Rake angle: increase rake angle, decrease the deformation of cutting, cutter force and cutting temperature. But it can not be too large, or the life time of cutting tool will be shorter.
Clearance angle:the main function of the clearance angle is to decrease the friction between the major flank and the workpiece. Increasing the clearance angle can decrease the friction, make the machined surface have better quality, and make the life of the cutting tool longer. But it can’t be too large as well, or it will affect the cutting heat, there will be too small area to abstract the heat.
Cutting edge angle: decreasing the major cutting edge angle and the minor cutting edge angle can decrease the roughness of the surface, increase the strength of the tool nose and the life time.
Tool cutting edge inclination: changing the tool cutting edge inclination can change the direction of the chip flow.
Machining method in mechanical manufacturing:
According to the change of the mass of the material △m,
If △m<0, it is material removal process, such cutting, milling;
If △m>0, it is material accumulation process, such as welding, casting;
If △m=0, it is material forming process, such as forging(锻造).
The model of the machine tool:
The model of the machine tool includes base part and auxiliary part.
For example,
Fixture(夹具):
The function of the fixture:
1, decrease the mismachining tolerance, increase the work accuracy;
2, increase production efficiency;
3, decrease the labor intensity;
4, widen the work range of the machine tool;
The component of the fixture:
1,setting element(定位元件); 2,clamp device(夹紧装置);
3, the tool components(对刀元件); 4, connecting element(连接元件);
5,other elements(其他元件); 6,specific folder(夹具体).
The fixture should limits six degree of freedom of the workpiece.
This part will introduce in《Course exercise for basis of Manufacturing Technology》.
参考：来源：大三大四专业课资料（英文.docx｜专业：机械工程｜课程：机械制造技术基础